Doc :read-write checkbox in "CSS features reference"

[mikehoffms]

todo: before merge, maybe comment-out Pending headings, and those links in local TOC.

Rendered article section for review:

• CSS features reference > Toggle a pseudo-class
  • /devtools/css/reference.md
  • Internal preview: https://review.learn.microsoft.com/microsoft-edge/devtools/css/reference?branch=pr-en-us-3625#toggle-a-pseudo-class
    • Upstream: https://developer.chrome.com/docs/devtools/css/reference/#pseudo-class
  • External preview: https://github.com/MicrosoftDocs/edge-developer/blob/user/mikehoffms/hov-pseudo-class/microsoft-edge/devtools/css/reference.md#toggle-a-pseudo-class
  • Before/live: https://learn.microsoft.com/microsoft-edge/devtools/css/reference#toggle-a-pseudo-class
  • Added Force specific element state expander & its :read-write checkbox.
  • Updated the headings outline per latest upstream.
    • Added upstream url comment under each heading.

AB#55537305

[captainbrosset]

We should hide the new empty sections for now and open a new ADO item to catch up with upstream.

[mikehoffms]

LGTM - Writer/Editor

[learn-build-service-prod]

Learn Build status updates of commit b30562e:

✅ Validation status: passed

File	Status	Preview URL	Details
microsoft-edge/devtools/css/reference-images/css-elements-styles-hov-hover.png	✅Succeeded	View
microsoft-edge/devtools/css/reference-images/format-icon.png	✅Succeeded	View
microsoft-edge/devtools/css/reference-images/specific-pseudo-classes.png	✅Succeeded	View
microsoft-edge/devtools/css/reference.md	✅Succeeded	View

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